As known in the art, a DRAM device includes numerous memory cells, and each memory cell stores one bit of information. A memory cell typically consists of a capacitor and an access transistor. One source or drain region of the access transistor is connected to one of the capacitor terminals. The other source or drain region and the transistor gate electrode are connected to a bit line (or a digit line) and a word line, respectively. In addition, the other capacitor terminal is connected to a reference voltage. Therefore, it is important to provide a proper electrical connection between components of the devices for operation. Such connections between device components can be made by contacts formed in the insulating layer.
With recent advances of semiconductor manufacturing techniques, design rules are getting smaller and smaller for semiconductor devices. As a result, alignment margin is difficult to secure, especially when aligning contacts between closely spaced conductive lines. As semiconductor devices become highly integrated, a contact margin between a digit line contact plug and a digit line contact area have been decreased, generating limitations such as misalignment or overlay issues, for example, cell contact to digit line contact overlay, digit line to digit line contact overlay, and storage node to cell contact overlay.
Further, as the landing areas for forming the digit line contact and cell contact become smaller and smaller because of the shrinking active areas in the memory array, the contact resistance increases dramatically, especially when misalignment occurs.